This invention relates to roadway surface reconditioning apparatus and more specifically to a machine for scarifying and in-place recycling of asphalt or like bituminous road surfaces.
The term "scarifier" is used herein to denote a machine that travels slowly along a roadway while heating the existing asphalt to a relatively high temperature. It then loosens the hot asphalt with a scarifying assembly to a depth of typically about an inch. Finally it smooths down the loosened hot material to form a reconditioned and resurfaced roadway. In some cases a liquid rejuvenator and/or new asphalt can be added before the smoothing stage. The scarifier is followed by a roller for further compressing the material while it is still relatively hot.
A typical prior scarifier is disclosed in U.S. Pat. No. 3,989,401 issued Nov. 2, 1976 to F. F. Moench.
A critical part of such a machine is a heater assembly for applying heat to the old roadway surface. It is desirable to apply as much heat as possible to the asphalt, and to do so as quickly as possible, because the amount of heat that can be transferred to the asphalt per unit time will determine how fast the machine can travel along the road and hence how many miles of road one machine can treat in a day. The efficiency of heat transfer will also determine the depth to which the asphalt can be heated to the extent required to enable it to be loosened by the scarifying teeth. For example, existing machines can typically travel at about 15 feet per minute, based on treating at the most the top one inch of asphalt. Such operation would require a maximum heater output of about 60,000 BTU per square foot per hour.
Many past attempts to increase the amount of heat transferred to the roadway surface have resulted in either setting fire to the asphalt or burning it to such an extent that it could no longer be reused without extensive reconditioning. Machines of this type have also been blamed for starting fires among shrubs and other vegetation along the side of the road, due to uncontrolled excessive heat.
Another problem that has been experienced in these machines in the past is adaption of the scarifying assembly to variations in roadway surface conditions, especially irregular profiles and widths.